1. Field of the Invention
The invention relates to optical amplifiers and oscillators, and in particular to solid state lasers such as semiconductor diode lasers (SDL's) and fiber amplifiers in which the amplified light is confined to propagate in optical waveguides.
2. Description of the Prior Art
The amplifiers in issue here employ waveguides and depend for confinement not on total internal reflection from the index of refraction or discontinuity or gradient of the index as is the usual case, but rather on Bragg reflection from an artificially rendered periodic or quasi periodic medium. Such waveguides were first proposed and analyzed in 1976, and demonstrated in 1977 in planar geometries. An extension of this idea to fibers with a circular cylindrical geometry took place in 1978.
FIGS. 1, 2a, 2b, 3, 4a and 4b illustrate generically, a conventional dielectric waveguide, a fiber waveguide, a transverse Bragg waveguide and a Bragg confined fiber respectively. FIG. 1 a diagrammatic perspective view which shows a waveguide where n2>n1 of the surrounding material and where the light bounces down the waveguide and is confined by the discontinuity in the index of refraction. FIG. 2a a diagrammatic perspective view of a planar realization of transverse Bragg waveguide layers. FIG. 2b a diagrammatic perspective view of an embodiment where the planar alternating periodicity is due to a corrugated wavy interface of an epitaxially grown layer. FIG. 3 is a diagrammatic perspective view of a conventional clad optic fiber where n2>n1. FIG. 4a a diagrammatic perspective view of a cylindrical Bragg fiber where light is guided in the core and is Bragg reflected at the interface. FIG. 4b a diagrammatic perspective view of a waveguide where the index contrast between two adjacent layers is realized using longitudinal bores longitudinal bores which are empty or filled.
A recent paper by the inventor shows that periodic waveguides require that the width w of the periodic channel must be related to the unit cell dimension b. In the simplest case of a small index perturbation where Δn<<n, w=b/4.